Enterovirus 71 (EV71) is an emerging picornavirus that has become endemic in Asia-Pacific regions. EV71 infection commonly manifests in childhood as an exanthem known as hand, foot, and mouth disease (HFMD), but in children under the age of 5, severe complications may occur, such as brainstem and/or cerebellar encephalitis, aseptic meningitis, and acute flaccid paralysis. The most devastating complication of EV71 neurologic disease is neurogenic cardiac failure with pulmonary edema. This syndrome can be fatal within hours of onset. There are no specific anti-viral drugs or vaccines approved for EV71 disease. But, in endemic areas, intravenous immunoglobulins (IVIG) are a standard component of supportive care, as IVIG in those regions have significant EV71 IgG titers. Should EV71 spread to non-endemic areas, such as the United States, IVIG will not be useful due to low EV71 IgG titers. Essentially nothing is known about the human antibody response to EV71 at the level of individual antibodies. The objective of the research is to characterize the human neutralizing IgG response to EV71 in subjects who have survived endemic EV71 infection in Taiwan. Two innovative techniques will be used for studying the human antibody response to EV71. A proteomics approach will identify the specific EV71-reactive IgG clonotypes found in sera of naturally infected EV71 patients. This method is an innovative combination of protein mass spectrometry and a NextGen sequencing method that preserves natural HC:LC pairing. Concurrently, a novel hybridoma method of human antibody cloning will functionally screen human mAbs from the same patients in order to identify those with EV71 neutralizing activity. Correlation of these combined datasets will allow an assignment of functions to the exact antibodies present in the serum repertoire. This unprecedented level of detail about the human anti- EV71 antibody repertoire will enable studies to understand the function of antibodies in protection from EV71, including structural studies and animal modeling. The research will seek to identify pairs of non-cross-resistant mAbs with broad-spectrum neutralization activity that will establish proof-of-concept for an EV71 therapeutic intended for use in the USA.